The present invention relates to a plastics sorting apparatus for sorting plastic chips obtained by fragmenting disposed plastic articles.
In recent years, the commitment to recycling garbage has been growing fast. The most common types of plastic that are consumed as raw material for plastic articles are vinyl chloride resin, polyethylene resin, polypropylene resin and polystyrene resin, and it seems that they account for major part of disposed plastics that are collected. To recycle such plastics, it is necessary to separate them by type.
Conventionally, a plastics sorting apparatus 50 as shown in FIG. 5 is used to sort plastic chips containing a plurality of different types of plastics as mentioned above. This plastics sorting apparatus 50 includes a charging device 52 and an electrostatic sorting apparatus 55. The charging device 52 charges batches of a predetermined amount of fragmented chips of different types of plastic while stirring them. The charged plastic chips 51 are then sorted by passing between a metal drum electrode 53 and an electrode plate 54.
The main section 56 of the charging device 52 is provided with an insertion portion 57 and an ejection portion 58. Inside the main section 56, a stirring member 59 is provided for stirring the plastic chips 51 that have been inserted into the main section 56 through the insertion portion 57. Above the insertion portion 57, a belt conveyer 60 is arranged so as to supply chips of fragmented plastic 51. The charging device 52 performs batch processing, which means that after the predetermined amount of plastic chips 51 has been stirred for a certain time, a batch of charged plastic chips 51 is ejected from the ejection portion 58 onto the metal drum electrode 53.
The metal drum electrode 53 is freely rotatable. Moreover, the electrode plate 54 is fastened in opposition to the metal drum electrode 53. An anode of a high-voltage power source 61 is connected to the metal drum electrode 53, and a cathode of the high-voltage power source 61 is connected to the electrode plate 54. This builds up an electrostatic field for sorting between the metal drum electrode 53 and the electrode plate 54. A first collecting container 62 and a second collecting container 63 are arranged below the metal drum electrode 53.
The following is an explanation of how this configuration operates.
A batch of a predetermined amount of fragmented plastic chips 51 is dropped from the belt conveyor 60 into the main section 56 of the charging device 52. Inside the main section 56, the different types of plastic chips 51 are stirred for a certain period of time and are charged by being rubbed against one another. The charged plastic chips 51 are then ejected in batches from the ejection portion 58 of the charging device 52 onto the peripheral surface of the rotating metal drum electrode 53. Those plastic chips 51 that have been charged positively are repelled by the metal drum electrode 53 and attracted by the electrode plate 54, and fall into the first collecting container 62. Those plastic chips 51 that have been charged negatively are attracted by the surface of the metal drum electrode 53, and fall into the second collecting container 63, due to the rotation of the metal drum electrode 53.
While the plastic chips 51 are being stirred in the main section 56 of the charging device 52, no new plastic chips 51 are fed by the belt conveyor 60. After the plastic chips 51 have been stirred for a certain time and all plastic chips 51 have been ejected from the ejection portion 58 of the charging device 52, the next plastic chips 51 are fed from the belt conveyor 60 to the charging device 52.
However, in this conventional apparatus, the charging device 52 performs batch processing, which means that after a predetermined amount of plastic chips 51 has been stirred for a certain time, a batch of charged plastic chips 51 is ejected. Therefore, a large amount of plastic chips 51 is ejected from the charging device 52 onto the peripheral surface of the metal drum electrode 53 each time, and there is a danger that the plastic chips 51 accumulate on the peripheral surface of the metal drum electrode 53 to form a layer that is thicker than is appropriate for electro static sorting. This poses a problem that the plastic chips 51 between the metal drum electrode 53 and the electrode plate 54 cannot be accurately sorted anymore.
It is therefore an object of the present invention to provide a plastics sorting apparatus capable of adjusting the feeding amount of plastic chips during the feeding of charged plastic chips onto a movable electrode so as to optimize the electrostatic sorting.
A plastics sorting apparatus in accordance with the present invention includes:
a charging device for charging a batch of a certain amount of different types of fragmented plastic chips while stirring the plastic chips, and
an electrostatic sorting device for sorting plastic chips that have been charged with the charging device by passing them between a pair of sorting electrodes, characterized in that:
the charging device ejects a batch of plastic chips after stirring the plastic chips for a certain period of time T that is necessary to charge the plastic chips;
one of the pair of sorting electrodes is a stationary electrode, and the other of the pair of sorting electrodes is a movable electrode that is arranged to oppose the stationary electrode and adapted to rotate at a peripheral speed v;
the apparatus further comprises
a first feeding device for feeding batches of a feeding amount W1 of the plastic chips to the charging device; and
a second feeding device for continuously feeding onto the movable electrode of the electrostatic sorting device a feeding amount per unit time W2 of plastic chips that have been ejected in batches from the charging device; and
the feeding amount per unit time W2 can be adjusted so as to satisfy
W1/Txe2x89xa6W2xe2x89xa6vxc3x97Bxc3x97Hxc3x97D
where B is a width of the movable electrode, H is an average thickness of the plastic chips that have been fed onto the movable electrode, and D is a bulk density of the plastic chips.
With this configuration, the first feeding device feeds batches of different types of fragmented plastic chips in feeding amounts W1 to the charging device, and the charging device stirs and charges the plastic chips for a certain period of time T. Then, the plastic chips are ejected in batches from the charging device, fed at a feeding amount per unit time W2 by a second feeding device onto the movable electrode of the electrostatic sorting device, and pass between the rotating movable electrode and the stationary electrode. By this, the plastic chips are separated into positively charged plastic chips and negatively charged plastic chips.
In this process for sorting the plastic chips, by satisfying W1/Txe2x89xa6W2, after all the batch of plastic chips that have been ejected from the charging device are fed by the second feeding device to the movable electrode, the next (successive) batch of plastic chips is ejected from the charging device and fed by the second feeding device to the movable electrode. Thus, it can be avoided that, while first plastic chips that have been ejected from the charging device are being fed to the movable electrode with the second feeding device, successive plastic chips that are ejected later are added to the first plastic chips that are still in the second feeding device. Consequently, such a problem can be avoided that plastic chips pile up between the charging device and the second feeding device.
Moreover, by satisfying W2xe2x89xa6vxc3x97Bxc3x97Hxc3x97D, the feeding amount of plastic chips can be set optimally for electrostatic sorting, and the plastic chips that have been fed to the movable electrode form a layer on the movable electrode that has a suitable thickness for electrostatic sorting. Thus, it can be prevented that the plastic chips accumulate and form a layer that is thicker than is appropriate for electrostatic sorting.
In accordance with the present invention, it is preferable that the charging device includes a rotatable stirring member for stirring the plastic chips, and a feeding amount detector for detecting a feeding amount of the plastic chips that have been fed in batches from the first feeding device, wherein the first feeding device is a conveyor and the second feeding device is a screw feeder, and wherein the plastics sorting apparatus further comprising a control unit for controlling driving devices for driving the conveyor, the stirring member, the screw feeder and the movable electrode depending on a feeding amount that is detected by the feeding amount detector.
With this configuration, a control device controls the driving devices such that W1/Txe2x89xa6W2xe2x89xa6xc3x97Bxc3x97Hxc3x97D is satisfied, when the feeding amount of the plastic chips that are fed in batches from the conveyor to the charging device increases or decreases.
In accordance with the present invention, it is preferable that the plastics sorting apparatus further includes a shutter for opening and closing an ejection portion of the charging device.
With this configuration, the ejection portion is closed with the shutter, while the plastic chips are being stirred inside the charging device. Thus, insufficiently charged plastic chips are not ejected inadvertently through the ejection portion. Then, after the plastic chips have been stirred for a certain period of time T, the shutter opens the ejection portion, ejecting a batch of sufficiently charged plastic chips through the ejection portion.